Which one of the following statements is NOT correct? (a) The presence of NaCl increases the rate of setting of plaster of Paris
Which one of the following statements is NOT correct?
(a) The presence of NaCl increases the rate of setting of plaster of Paris
(b) Gypsum is added to the cement to slow down its rate of setting
(c) All alkaline earth metals form hydrated salts
(d) Barium and strontium are found free in nature
1 Answers
(d) Barium and Strontium are alkaline earth metals. They are quite reactive in nature, they do not occur in free state. Strontium is a relatively abundant element in the Earth's crust. The most common minerals containing strontium are celestine and strontianite. Celestine contains primarily strontium sulfate (SrSO4), while strontianite contains mostly strontium carbonate (SrCO3). The most common naturally occurring minerals containing barium are the very insoluble barium sulfate, BaSO4 (barite), and barium carbonate, BaCO3 (witherite).